X-ray tubes include an anode. High energy electrons impact the anode driven by a voltage drop between the anode and a cathode. A small part of the energy of the high energy electrons is converted into X-rays. The rest of the energy must be removed by cooling.
This cooling may be carried out using a heat spreader. The overall heat transfer coefficient is important. Therefore, heat spreader materials with a high thermal conductivity are necessary to keep the anode temperature as low as possible. As the power of the X-ray tube rises, high temperatures cannot be avoided. It is still however necessary to keep the anode temperature low enough to prevent evaporation or melting of the anode material.
Thus, the environment of the anode in an X-ray tube can be very harsh-temperatures can be high and x-ray intensities also very high. It is necessary to maintain good anode function in this harsh environment. In particular the harsh environment does not simply include high temperatures of 800° C. or higher but also high temperature gradients.
Conventional heat spreader materials are copper or silver which are selected because of their high heat conductivity. However, such materials can have thermal expansion mismatches with the anode material which can lead to high stresses.
Selection of alternative materials is not easy, since it is not sufficient to simply choose another heat spreader material. It is also necessary to fix the anode securely to the heat spreader in such a way that the anode remains firmly attached with a low thermal resistance even in the challenging environment of an X-ray tube, and suitable ways of fixing the anode have not been previously identified. Accordingly, X-ray tubes continue to use copper or silver heat spreaders.